The plan is to investigate the biochemical mechanisms of hlycogen metabolism and metabolic significance of glycogen in rat epididymal adipose tissue: its depletion on fasting and in diabetes and its excess deposition on refeeding, espeically a diet with a high carbohydrate content. The relative significance of three types of regulatory mechanisms will be evaluated: covalent modification of enzymes (phosphorylation by protein kinases), substrate-regulated control, viz, allosteric effectors, and the physical association of glycogen metabolism and of glycolysis with their macromolecular substrate (the glycogen particle). Rats will be given specific courses of nutrition, epididymal fat pads removed under anesthesia, and properties of the control mechanisms mentioned above will be evaluated in the presence of insulin, epinephrine and other hormones. A major hypothesis that will be tested is that the structure, degradation, and regeneration of the glycogen particle is significant in control of the supply of 3-glycerophosphate, the endogenous substrate for triglyceride synthesis. therefore changes in the diet composition and feeding pattern may markedly affect the metabolic control mechanisms that determine triglyceride storage, obesity, and responses to diabetes of adipose tissue.